1. Field of the Invention
The present invention concerns a method and device for coding images representing views of the same scene.
The invention is situated in the technical field of image coding, and in particular in the field of the coding of multiple views of the same scene.
2. Related Art
The future MVC (the acronym for Multi-View Coding) video coding standard developed by the JVT (Joint Video Team) group of ISO/IEC MPEG and ITU-T VCEG aims to define a format for coding video sequences coming in particular from several cameras in a single bitstream, the number and spatial positioning of these cameras being able to be variable. The sequences may also be synthetic video sequences that are stored prior to coding to the MVC format.
The video coding proposed in the context of MVC is based on the MPEG4-AVC format, also referred to as H.264, which has good performance in terms of video compression. The specificity of MVC compared with H.264 is the possibility of simultaneously coding several views of the same scene. In order to improve the efficacy of compression and to take account of potential redundancies between views, it has been proposed to code the images of sequences representing the views in a dependent manner, by defining in particular a so-called principal view that serves as a reference for the other views. These other views, referred to as secondary, are coded in a coding dependency structure with respect to the principal view. Subjective tests have shown the gain in this approach compared with a coding of views carried out independently.
Firstly, the principal view and the position of the secondary views in the coding dependency structure were chosen in an arbitrary manner, the principal view being for example the view of the first camera, the first secondary view corresponding to the view of the second camera and so on.
The JVT-102 technical contribution entitled “Results on CE1 for multi-view video coding”, by Sohn et al, presented at the Klagenfurt meeting of 17-21 Jul. 2006, proposes a structure in which the sequence corresponding to the principal view is chosen according to a criterion of disparity between the sequences. The disparity is calculated between the adjacent sequences and the sequence chosen as the principal view is that having a disparity with the adjacent sequences corresponding to the median of the disparities calculated. The arrangement of the other sequences being coded according to the predictive (P) or bidirectional (B) coding mode is determined solely according to the distances between the photographic cameras with respect to the camera relating to the principal view. This method has the drawback of calculation complexity for the choice of the principal view. With regard to the choice of the secondary views, their arrangement does not make it possible to end up with an optimized coding in terms of compression.